In building construction, electrical receptacle boxes are mounted on upright wall studs, either metal or wood, in order to mount an electrical receptacle, such as an outlet or a switch, and associated electrical conduit and the like. The box can be fixed directly to the stud by nails, screws or other arrangements, or can be fixed on clamping members fastened between adjacent studs. The front plane of the box opening is generally flush with the front surface of the wall studs. A mounting cover or frame is fixed to the recepatacle box, and the receptacle is mounted to the frame. The front of the frame is forwardly offset from the front face of the box in order to accommodate the thickness of wallboard to be installed on the wall studs whereby the receptacle will be generally flush with the outer surface of the wallboard. Such a frame is sometimes caled a mounting ring or mud ring.
Difficulty is frequently encountered in correctly positioning the receptacle box and mounting frame whereby the electrical receptacle is properly flush with the wallboard or construction panel when mounted on the wall studs. Vagaries of the various box-mounting methods may leave the front face of the box slightly askew or depressed with respect to the intended planar surface of the erected wall. The wall stud itself may be slightly askew producing the same result. This necessitates compensation through the use of shims or other undesirable contrivances to attempt to bring the electrical receptacle into proper flush relation with the exposed surface of the erected wallboard.